Optical Coherence Tomography in Cornea and Refractive Surgery

Volkan Hurmeric; Sonia H Yoo; Fatih Mehmet Mutlu

Disclosures

Expert Rev Ophthalmol. 2012;7(3):241-250. 

In This Article

Ultra-high-resolution OCT

Ultra-high-resolution (UHR) OCT is a new imaging system that uses broadband light sources and has an axial resolution below 5 µm in tissue. It has been used in several clinical and scientific laboratory research purposes such as evaluation of tear fluid dynamics, etiology of contact lens-associated dry eye, contact lens fitting and imaging of corneal structures.[67–70] The image qualities of these prototype systems are similar to an optical biopsy. UHR-OCT has been used to describe the characteristics of epithelium, stroma and Descemet membrane in corneal degenerations and in healthy eyes.[71]

Morphological studies in corneal degenerations have been performed in advanced cases that required penetrating keratoplasty.[72] However, UHR-OCT can be used to analyze in vivo morphology of the cornea without tissue sampling.[73,74] This novel system demonstrates new morphological properties of corneal disorders. In Salzmann nodular degeneration, the presence of an intact Bowman layer was suggested to be a predictor of the strength of the adhesion of the superficial lesion to the underlying stroma.[73] This finding has been suggested to be useful in presurgical planning of the excision of the nodules in Salzmann nodular degeneration.

UHR-OCT is an objective technique that can be used in the diagnosis and management of conjunctival intraepithelial neoplasia.[75] It can be used in subclinical cases to demonstrate the location and extend of the disease. UHR-OCT can also be used in the follow-up of these patients undergoing medical treatment or surgical excision.

UHR-OCT has the potential to be used in refractive surgery as an adjunctive tool to prevent complications and for in vivo morphological analysis. It can be used in several problems encountered during femtosecond laser-assisted surgery in which histological analysis is technically impossible. One of the recent clinical applications of UHR-OCT is the evaluation of the opaque bubble layer (OBL).[76] OBL is the accumulation of gas bubbles in the corneal stroma during femtosecond laser-assisted LASIK flap creation. Although OBL disappears in several minutes, it can interfere with the eye tracking system of the excimer laser and may cause incomplete islands in some femtosecond laser platforms. UHR-OCT demonstrates OBL as bright white areas, located in the mid-stroma. OBL located above the flap interface has been observed in patients with undissected flap zone. This pattern of OBL has been suggested to be a contraindication to flap lifting.[76]

Serious flap-related complications can occur in femtosecond laser assisted LASIK.[77,78] Suction loss, corneal scars and OBL are the main reasons for these complications. One of the major advantages of the femtosecond laser is the ability to prepare a second pass in the same eye after suction loss. If the flap lift is aborted, serious flap complications can be avoided by this method in selected cases.[79,80] UHR-OCT imaging can be performed to analyze the flap integrity in cases with suspected flap problems before flap lift is attempted.[81] Indistinct flap interface or epithelial breakthrough in UHR-OCT may suggest preparing a second pass in these cases. Future studies are required to confirm these data and clinical applications of this new imaging system in refractive surgery.

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